Anaphylaxis is a severe allergic reaction that can be rapidly progressing and fatal. In instances where the triggering allergen is not known, establishing the cause of anaphylaxis is pivotal to long-term risk management. Determining the trigger is limited, however, to known causes of anaphylaxis. Therefore, identification of novel causative agents will provide an important step forward by reducing risk of disease and facilitating new, specific treatment approaches. The overarching hypothesis for this proposal is that IgE antibodies to carbohydrates are a major factor in anaphylaxis that currently appears to be idiopathic. We have recently identified and described a carbohydrate, alpha-gal, as a novel food allergen. Patients who have IgE antibodies to alpha-gal report delayed anaphylaxis or urticaria occurring 3-6 hours after eating beef, pork or lamb. The significance of investigating these reactions comes not only from the obvious importance of understanding a novel life threatening form of food allergy, but also because of the possibility of defining a totally new mechanism for reactions related to an important food substance. Our plan of research will investigate the relationship of IgE antibodies to alpha-gal with anaphylaxis and determine whether these antibodies are specific for the carbohydrate alpha-gal. A delay of 3-6 hours is most unusual in patients with classical food allergy and warrants investigation of the mechanism(s) involved. Using histamine release and basophil activation studies, we will determine whether IgE to alpha-gal can be functionally activated in these cells. Following the completion of the mechanistic studies, we will perform double-blind, placebo controlled food challenges to further understand the delayed appearance of clinical symptoms after eating mammalian meat. Most patients who have IgE to alpha-gal tolerated mammalian meat for many years prior to the onset of symptoms. Interestingly, greater than 90% of patients in our cohort who have IgE to alpha-gal report being bitten by large numbers of adult or larval ticks ('seed ticks') in the weeks or months prior to developing symptoms. Using dendritic cell (DC) and T cell co-culture, we will test the hypothesis that a specific receptor, that of the type II C-type lectin receptor, is critical to the initiation of a TH2 response to the tick antigen. Our current work has shown that IgE to the carbohydrate alpha-gal is present in a cohort of patients who report delayed anaphylaxis and allergic reactions after eating mammalian meat. We believe that IgE to alpha-gal and other carbohydrates represents a novel cause of food allergy. The specific aims outlined in this proposal are designed to establish the specificity of this carbohydrate-directed IgE (Specific Aim #1), elucidate the functional role of this IgE in food allergy (Specific Aim #2) and elucidate the mechanism for induction of TH2 responses which govern IgE antibody production to this moiety (Specific Aim #3). Anaphylaxis, or shock, is a severe allergic reaction that can progress quickly and may be fatal if appropriate medical action is not taken. We have identified a group of patients in the Southeastern U.S. who develop delayed anaphylaxis 3-6 hours after eating beef, pork or lamb and appear to be allergic to a sugar on red meat. Because of the delay, their symptoms would normally be regarded as 'spontaneous'or 'of unknown cause'but understanding why the delay occurs and why adult patients in the Southeast are suddenly becoming allergic to red meat may provide real insight into the factors that control anaphylaxis and food allergy.